As a representative of the traditional building materials, concrete has its inherent advantages of compressive strength, high durability and low cost, therefore being widely used in industrial and civil buildings, bridges, road works, underground works, water conservancy and hydropower projects, nuclear power plants, ports and ocean engineering structures. Currently, the concrete is used in the large-span structures, high-rise structures, mega-structure and the special structure as the most widely applied material that has more than 100 years of history.
In the foreseeable future, the concrete is still an indispensable building materials in the country's modernization construction. In-service concrete structures due to the use of long-term process and under the influence of the surrounding complex environment, will inevitably produce micro-cracking and local damage. Those defects usually would reduce the life of the structure, cause re-structure, even threaten safety. Therefore, the structural repair of cracks in concrete is a long-troubled technical problem to civil engineers. Researches on raw materials, mixing ratio, additives, manufacturing processes, casting processes do not fundamentally change the performance of weaknesses of the concrete. Therefore, to repair the crack of the concrete in service timely and effectively has become a major concern of scientists and engineers. Due to damage caused by macro such as earthquakes, wind loads, shock, you can visually detect and fix it manually, using traditional methods (program repair and post-restoration) on the crack repair. In the actual structure of concrete works, there are many small cracks, such as micro-cracking of base body and so on, and these micro-scale damage may be undetectable due to the limitations of detection technology. Therefore, it becomes very difficult to repair these undetectable cracks and damage, if not impossible. If the cracks or damage can not be timely and effectively restored, the structure will not only affect the normal use of the performance and shorten the life, but also macro-cracks may be triggered and lead to structural brittle fracture, resulting in a serious catastrophic accidents. There is an urgent need to adopt a certain technology or method that can initiatively and automatically to repair and restore the cracks and damage, or even can increase the strength of concrete materials in order to achieve a purpose of extending the service life of concrete structures. Conventional concrete and method for fabricating concrete cannot make the solution of micro-cracks self-diagnose and self-repair.
The self-repair of the concrete is conducted by adding special components (such like shape memory alloy) to form intelligent self-repair system that can be automatically triggered to fix the damage or cracks of the concrete material.
Currently, researches about self-repairing concrete structures are concentrated in the hollow fiber restoration techniques. Although it is still in the laboratory stage, the hollow fiber capsules proof the function of the self-repairing concrete. However, the construction process of concrete causes vibrations, etc., which disturb the arrangement of hollow fiber capsule design, and even lead to rupture of the glass wall material, namely the premature loss of restorative, which is unable to attain the purpose of repairing concrete and affect the feasibility of self-repairing process of the concrete and the repeatability of self-repairing capacity of the concrete. During a process of oxidation and use, micro-cracks and cracks in concrete structures appeared in large numbers randomly. Self-repairing technique requires the repair capsules evenly distributed in the concrete structure. Because the hollow fiber material has restrictions due to the brittle characteristic, the hollow fiber capsules can not ensure micro-capsule material in concrete in the uniform distribution, so that the fiber capsule of the micro-cracks in self-repairing process of the concrete structure can only adopt special concrete materials and special technique. These difficulties limit the hollow fiber capsules in repair cracks in the concrete structure effectively. Surface properties, wall material strength, geometry parameters and content of hollow fiber capsule have significant impacts on the repair of concrete results. Fibrous capsule wall material is smooth and in lower bond strength of concrete that make concrete hard to form an effective phase interface. Hollow fiber capsule has larger size, sometimes up to millimeters in diameter and can be considered that fixed agents are introduced as well as defects, inevitably, in the concrete structure, which will reduce the concrete's own strength and self-repairing efficiency. Hollow fiber capsule wall material a large strength of glass, thus stress generated by the micro-cracks of the concrete may be difficult to provide enough energy to the make hollow fiber capsule rupture, and this technology may only fix large cracks while in critical factor of damages of the concrete structure, micro-crack, may be very limited for the micro-crack to be self-repairing. This shows that the method still has many problems to be solved in engineering applications, including durability of the fibrous capsule, timeliness of repairing, interface compatibility, reliability, and feasibility of restoration and other issues in engineering applications. It is obvious that early repair of micro-cracks is significant and essential for the durability of concrete structures, so that the use of hollow fiber micro-capsule technology does not fit micro-cracks repairing for reasons including the above-mentioned limitations.
What is needed, therefore, is a self-repairing concrete having polyurethane polymer micro-capsules. What is also needed is a method for fabricating such concrete.